The head of Arab League observers in Syria rejected criticism Monday that his team had failed to stop killing in the country, where thousands of people have died in clashes between government protesters and opposition forces demanding the end of President Bashar al-Assad's regime.

Sudanese Gen. Mohammed Ahmed al-Dabi said Monday at a news conference in Cairo that the mission was designed not to bring an immediate end to violence but to investigate and observe the situation.

Rising concerns about the government's violent crackdown prompted the European Commission to widen sanctions Monday against Syrian officials and organizations. The group imposed asset freezes and travel bans on 22 more Syrian officials it said were responsible for human rights violations and eight entities that give financial support to al-Assad's regime.

"Today's decision will put further pressure on those who are responsible for the unacceptable violence and repression in Syria," said Catherine Ashton, the European Union high representative for foreign affairs. "The message from the European Union is clear: The crackdown must stop immediately. We will continue to do all we can to help the Syrian people achieve their legitimate political rights."

Violence in the country has continued despite the presence of the Arab League team.

An officer in the opposition Free Syrian Army told CNN early Tuesday that a bombardment by the Syrian army "with heavy artillery and mortars" was underway in the Damascus suburb of Douma. The bombardment had been going on for an hour, said Lt. Col. Mohamed Hamado.

Monday, five people died and 13 people were wounded when government forces and defectors clashed in Homs, according to the Syrian Observatory for Human Rights, an opposition activist group.

Another opposition group, the Local Coordination Committees of Syria, reported 12 deaths in Homs and a total of 36 killed across the country Monday. The dead included 11 in Idlib, another six in Daraa, four in Damascus and its suburbs, and one each in three other cities.

The government news agency SANA reported that three of the deaths in Homs were law enforcement personnel. The agency said nine army and law enforcement personnel died in cities across the country Monday.

CNN cannot confirm the claims of violence and deaths, as Syria's government restricts access by foreign journalists.

Despite the continuing violence, al-Dabi defended his team's work, saying that it was able to persuade the Syrian government to remove tanks from neighborhoods and to reduce the number of military and security teams deployed near demonstrations.

Observers documented 136 deaths and the release of thousands of detainees during the 20-day mission, al-Dabi said.

The Arab League voted Sunday to extend the monitoring mission while it works on a proposal seeking that al-Assad transfer power to his vice president following the formation of a national unity government.

The group's plan calls for the government to start talks with the opposition within two weeks and for the formation of a new government within two months. A new constitutional council would follow, as would a plan for parliamentary and presidential elections.

The proposal is the clearest statement yet from the Arab League on what the league's member states would like to see happen in Syria. The league plans to take the idea to the United Nations in a bid to build international support.

Monday, the German ambassador to the United Nations, Peter Wittig, said the Arab League decision to seek the international body's endorsement was "really a bold step."

"We believe now more than ever that we need strong council action, a clear message to both the Syrian regime and the Syrian people," Wittig said at a press briefing at the German ministry. "Only real support and endorsement of the Arab League's decisions will do."

The British mission to the United Nations also said Monday it backs bringing the issue before the Security Council.

"We continue to believe that the Security Council must act in response to the ongoing violence taking place in Syria," the mission said in a statement. "We will work with partners in the Security Council to press for a robust U.N. response to allow the U.N. to act in support of the Arab League plan."

The Syrian government has roundly rejected the plan, which it views as "blatant intervention in its internal affairs," SANA reported. It was unclear if it would accept the monitoring team extension.

The United States put pressure on Syria on Monday to improve the situation, with or without any plan.

"It is not the job of the monitors to stop the violence -- it is the job of the Assad regime to stop the violence," U.S. State Department spokeswoman Victoria Nuland said Monday. "It's the job of the Assad regime to pull back its tanks, to allow journalists in, to release people from prison."

She said the United States may close its mission in Syria if the security issues are not addressed.

The uprising against al-Assad's regime, and the resulting government crackdown, have engulfed the country for more than 10 months. The United Nations last month estimated more than 5,000 people have died since March; opposition groups put the death toll at more than 6,000.

The Arab League has called on al-Assad's regime to stop violence against civilians, free political detainees, remove tanks and weapons from cities, and allow outsiders, including the international news media, to travel freely in Syria.

Secretary-General Nabil el-Araby said the Syrian government has not complied with some parts of its agreement with the league aimed at ending the violence. But Arab League monitors have seen some aspects of the situation improve, he said.

"The presence of the Arab monitors provided security to opposition parties, which held an increase in number of peaceful protests ... in the areas where the monitors were present," el-Araby said.

Burhan Ghalioun, head of the opposition Syrian National Council, said observers haven't been allowed to see the full situation in Syria.

"The Arab monitors indicated that the regime did not follow protocol, did not release the detainees, did not remove all military tanks, did not allow press to travel freely, did not recognize even once the peaceful protests, and the massacre of Idlib yesterday is proof of that," he said, referring to the discovery of 30 bodies in that city on Saturday. "The regime let down the Arab League, and Arab nations have the responsibility to respond."